In certain applications, for example in devices for continuously levelling metal strips, use is made of rollers which revolve about an axis, but which cannot, for various reasons, be fixed onto bearings designed to hold them in position, because they must have a degree of freedom in the axial direction and must merely be supported radially in their working position. Such a roller is therefore mounted so as to rest on roller wheels or on a support roller and its rotating shaft is equipped, at its ends, with axial bearings which come into contact in both directions with bearing plates mounted on the support frame, depending on the axial stresses exerted in various directions during operation. Normally, each bearing consists of a ball mounted at one end of the rotating shaft of the roller and capable of applying pressure against a suitably shaped wear plate mounted in the desired position on the frame. The ball revolves together with the roller when it is not exerting pressure, but stops very rapidly when it comes into contact with the wear plate. It is therefore fixed onto a support mounted rotatively about the axis of rotation, at the end of the shaft. The devices used for this purpose until now have proved satisfactory for speeds of up to 3500 rpm. However, it has now become necessary to consider much higher speeds of rotation, of the order of 10 to 12,000 rpm, and the inertia of the revolving support is, in such cases, too great to allow it, under favorable conditions, to stop rotating when the ball comes into contact with the frame.